linux-kernel - Re: [RFC][v4][PATCH 0/7] clone_with

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Date:	Wed, 12 Aug 2009 20:45:43 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, Oren Laadan <orenl@...columbia.edu>,
	serue@...ibm.com, Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
	Containers <containers@...ts.linux-foundation.org>,
	sukadev@...ibm.com, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC][v4][PATCH 0/7] clone_with_pids() system call

Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com> writes:

> === NEW CLONE() SYSTEM CALL:
>
> To support application checkpoint/restart, a task must have the same pid it
> had when it was checkpointed.  When containers are nested, the tasks within
> the containers exist in multiple pid namespaces and hence have multiple pids
> to specify during restart.
>
> This patchset implements a new system call, clone_with_pids() that lets a
> process specify the pids of the child process.
>
> Patches 1 through 5 are helpers and we believe they are needed for application
> restart, regardless of the kernel implementation of application restart.

I'm not very impressed.

- static int alloc_pidmap(struct pid_namespace *pid_ns)
+ static int alloc_pidmap(struct pid_namespace *pid_ns, int pid_max, int last_pid)

Do that.

That is pass in pid_max and last_pid, and you don't have to do weird
things in alloc_pidmap, and no set_pidmap is needed.

No changes to copy_process are needed it already takes a struct pid
argument.

I haven't been following closely what is gained by having a clone_with_pids
syscall?  

As for new namespaces that don't need to happen at process creation time
(which is just about anything that is left) we can create a new syscall that
unshares just that one.


Eric
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